Different clipping idea (I think?)

[composition4]

I came up with an idea with clipping diodes, and just want to know your thoughts.  Too lazy to breadboard it right now.  For the sake of this idea now, let's just simplify and talk as if it's one diode, not antiparallel diodes.

Assume a diode forward voltage of 0.7V.  With a standard forward biased diode from signal to ground, the part of the guitar signal above 0.7V above cathode of the diode (Ground, 0V) will be clipped off.  Now lets assume that the cathode was connected not to ground but to a signal of 0.5V.  Now the guitar signal would clip at 0.7V above the cathode voltage, hence will clip at 1.2V.  Obviously if there was an antiparallel diode, the negative portion of the signal would now clip at -0.2V, but I'm not thinking of that at the moment.

Now let's say that instead of the diode's cathode being connected to a fixed reference, it is connected to a low impedance sine wave - for example, 100hz 2V peak to peak (so going from -1V to 1V)

So the clipping amount would modulate depending on the voltage of the guitar signal compared to the voltage at the cathode of the clipping diode.  I'm thinking this might somehow cause intermodulation at the frequency of the sine wave reference, which could sound bad?  So instead, what if the cathode of the diode was connected to not a sine wave of fixed frequency, but a sine wave with varying frequency (i.e. a pure sine/triangle wave tracked from the frequency of the input signal, or the octave down/up of the input signal etc)?

Really not sure if this would really sound much different, but my thoughts are that once the idea is applied with two (anti-parallel) diodes, it would sorta end up switching itself between symmetric, to semi-asymmetric, to asymmetric clipping automatically - and would also vary the amount of clipping automatically, at a rate too fast to hear it directly?

Anyway, let me know your thoughts

Jonathan

[Quackzed]

thats an interesting idea..
my thinking is that if the modulation frequency were tracked from the input signal, it would behave in a dynamic way,
-whenever the input signal was high, the diode threshold would be high, when the signal was low the threshold would be low.
seems like it might provide some clipping while retaining dynamics...
if the modulation signal was steady i'd think it would behave as a sort of clean/distortion tremolo, fading  back and forth between louder clean signal to quieter distorted signal?

[R.G.]

Congratulations. You have invented the basis of the diode-clamped wave shaper.

Which was well known since at least the 1960's, probably before.

This is NOT a slight on you - you really did invent it without knowing the prior basis, just not first. This took as much effort as the original invention, and you were sharp enough to come up with it on your own.

[rosscocean]

Do you know of any clips RG? I'd like to hear this?

[composition4]

Thanks guys... So I guess it's not the newest idea around then, but I will at least breadboard a few things and see if I can get any interesting sounds!

Jonathan

[Quackzed]

i'd be interested to see any circuits that use this mechanism. I found this..
http://www.zap-tek.com/webpage/Elect/lsn_5/017_Diode_Approximations.html
which seems to fit the principal of your idea.
figured it may be usefull.

[Quackzed]

i wonder , is the 'bronx cheer', or the 'tytewadd ' from tim's 'circuit snippets' site using this mechanism by running diodes from collector to base of a transistor?
would a diode pair connected from a bipolar transistors collector to its base behave like this? ie, have a clipping threshold that is dependent
on the input signal strength?

[PRR]

> well known since at least the 1960's

All our inventions have been stolen by the Ancients.

Jonathan seems to have (re-)invented the diode-clamped wave shaper, which H-P ripped-off from him in 1965 (page 4 of hp journal Nov-1965, 3MB PDF).

Also a thing which generalizes as the Diode Mixer, also known as Ring Modulator.

As he keeps thinking he'll invent the diode attenuator, which CBS ripped-off from him around 1968 (and others stole it from CBS all through the 1950s and 1960s, and was probably known to Theremin).

I like that Jonathan invented de novo, because it means he can understand the basic how-it-works.

[DDD]

There was an old Russian DIY hi-gain stompbox with the clipping diodes connected to the rectified and filtered input signal voltage. Something like the "clipper with the dynamic clipping threshold dependent on the input voltage".
The guys who had it breadboarded report the sound is pretty "synthetic" with very long audible sustain.     

[Nasse]

http://gilmore2.chem.northwestern.edu/projects/limiter_prj.htm

[PRR]

http://gilmore2.chem.northwestern.edu/projects/limiter_prj.htm

That's a plain diode-clipper. The reference voltage is the annoyingly useful threshold of Silicon.

Jonathan has invented a diode plus another voltage source. Maybe battery, maybe another signal. The fact that others have used this idea already doesn't detract from it being a useful extension of basic diode wave-manglers.

[Lurco]

? http://www.diystompboxes.com/pedals/Elektor_variable_fuzz.PDF